Hi all,

I'm helping my dad convert a 19th century hay barn into a 3 bed home that he'll live in. We're aiming for Band A EPC, so a very high level of insulation and air tightness, if not quite PassivHaus standard.

We effectively have a blank slate, so I'm interested in the GBF hive mind's opinion on the best heating solution. We are expecting to use an air-source heat pump, and I know the most commonly done method is an air-to-water system, heating water for UFH and general use. However, there is no existing wet heating system and I'm interested in air-to-air systems, particularly ducted systems (not wall mounted units). My thinking is that it should be more efficient to use the warm air created by the ASHP to heat the home directly, rather than losing energy in converting warm air to warm water. Also, UFH is expensive to install and ducted air should be cheaper(?). I'm also interested in how it could interact with Mechanical Ventilation. I imagine it would add complexity, but for the money I've seen quoted for UFH, I'd guess you could get a very high-end warm air/ventilation setup.

I know warm air systems were wide spread in residential buildings in the 70s - but were not popular as I understand it. They are common in commercial buildings (HVAC) and I assume they have come along way in the last 50 years, but most contractors I speak to seem to be pushing wet UFH. I'm trying to understand if this is just 'what they're used to' installing, more profitable, or if it is genuinely a better solution.

I appreciate he'd need a separate solution for hot water if we use the warm air system. He has space for solar, or if not, would an electric water heater would do the trick, or would that negate the efficiency gains? I've seen this system which does both in another thread, but according to the Daikin installer I spoke to, it isn't yet available in the UK market. https://www.daikin.eu/en_us/product-group/air-to-air-heat-pumps/multiplus.htm

My dad is relatively open to both options, but I wouldn't want to push something on him that doesn't work well, or 'feel nice'.

The barn is in the South of England (Berkshire). I include plans, which I have permission to post.

I'd welcome your opinions, or alternatively suggestions of contractors that can help.

Thanks in advance!

Hello and welcome.

I wouldn't try to aim for any particular EPC band. It bears very little relation to the real world :( Personally I would suggest using PHPP since it is pretty accurate and measures something quantifiable and achievable. By all means pick a different target than PH level, but be aware of the differences if you do.

Posted By: TigoDogWe are expecting to use an air-source heat pump, and I know the most commonly done method is an air-to-water system, heating water for UFH and general use. However, there is no existing wet heating system and I'm interested in air-to-air systems, particularly ducted systems (not wall mounted units). My thinking is that it should be more efficient to use the warm air created by the ASHP to heat the home directly, rather than losing energy in converting warm air to warm water. Also, UFH is expensive to install and ducted air should be cheaper(?). I'm also interested in how it could interact with Mechanical Ventilation. I imagine it would add complexity, but for the money I've seen quoted for UFH, I'd guess you could get a very high-end warm air/ventilation setup.

A heat pump doesn't create warm air, it creates warm refrigerant. Whether that is changed into warm air or warm water depends on what type of heat exchanger is used indoors.

Posted By: TigoDogI know warm air systems were wide spread in residential buildings in the 70s - but were not popular as I understand it.

Indeed my first house, which I bought in the 1970s, had a warm air heating system, and it was fine for me since I lived alone and liked loud music, so I didn't care how much noise the heating system made. Most people do, and I would nowadays. The house I live in now is also heated by warm air, but the heating system is inaudible. The difference is that my house is a PH and needs so little heat that it can be heated by blowing warm air through the ventilation system. The PH standard was specifically chosen so that is possible! If you're not at that level, you won't be able to do it.

Looking at the plans (which it's not possible to see properly, unless there's some means to download them?) one immediate comment is that you'll have trouble meeting PH with the glazing arranged as it is. I can't tell which direction is north.

If you're thinking about a ventilation system and/or a warm air heating system, where will the ducts run? What type of joists and ground floor do you have?

I have a ducted air to air system and I wouldn't hesitate for a moment to install it again. The noise aspect isn't a problem IMO, if installed correctly. The system controls are excellent, as is the response time. Fitting registers with filters keeps circulating indoor air pleasant. The cooling option is a boon on the odd occasion. If there are areas where ducting becomes a bit difficult you also have the option of a large choice of other indoor air supply units. You will most likely need assistance with system design though.
With your "blank slate", the most onerous bit,- i.e. fitting and insulating the ducting,- is easily accomplished. On the water front I think too much is made of DHW supply. It's an easy problem to solve and again with your blank slate you have loads of cheaper options, that don't involve an expensive air to water unit.

These are the outdoor and indoor units. They are part of Toshiba light commercial range.

https://data.toshiba-klima.at/en/Super%20Digital%20Inverter%20R32%20-%207,10%20kW%20-%20R32%20-%20RAV%20RAV-GP801AT-E%20en.pdf

https://data.toshiba-klima.at/en/Standard%20duct%20unit%20R32_R410A%20-%207,10%20kW%20-%20R410A%20-%20SET64%20-%20RAV%20RAV-RM801BTP-E%20-%20RAV-GP801AT-E%20en.pdf



The indoor unit I immediately handed over to a local sheet metal company who fabricated inlet and outlet plenums each with two spigots for me to attach the initial ducting flows and returns. I suspended the unit from the rafters with threaded studs before directing the ductwork. In my case this was a pain because of my restricted attic roof-space, also because I chose to fit rigid spiral steel ducting in order to get smooth airflow.
The ducting overall is the difficult bit, both in fitting and design. I taught myself with some initial guidance from Paul in Montreal and by asking lots of questions from various suppliers and fitters.
Duct sizing and system design is a bit of a black art and I most likely erred on the side of caution which gave me extra grief. The end result however works fine and the oversized ductwork most likely aids any noise issues. I also had bespoke inlet and outlet ceiling registers and plenums made with removable filter medium screens.

It worked out fine in the end and because of the restricted attic space it was easiest to take two delivery and return ducting spigots. I was further hindered by only having ceiling space for both flow and return registers. On a new build I'd most likely put flows at floor level and returns in the ceiling and with modern rectangular ducting that's easily achievable into stud walls, but like I said room air movement and system design can be a bit of a black art.
In the end I think mine worked out OK.
I positioned one of the returns high up in the wall separating the glazed sun room from the sitting room. This allowed the system to drag in some warm roof level air which was then re-circulated aiding the overall system temperature modulation. In Summer if we use reverse cooling mode it keeps the sun room pleasant by dissipating any overheating.
I have no idea on the running costs because my home is virtually all electric and the thought of teasing out one device usage makes me queasy. I tend to simply round up incomings FITs, and outgoings power supply contracts and at the moment I live comfortably, and I'm still winning. Any wood I burn to supplement other non- A/A ducted areas or for occasional aesthetic reasons is from my own property tree prunings. Quite a bit of any heat so generated gets sucked into the A/A and is modulated as before.

Posted By: TigoDogUFH is expensive to install and ducted air should be cheaper [than ducted air heating](?)

I've not done a comparison, but I wouldn't expect there the be a huge difference. I've lived happily in homes with both systems, but personally I'd choose UFCH because it produces a very even temperature gradient in a room and a pleasantly warm floor to sit on. If the pipes are reasonably close together (minimum 150mm, it seems) it can be used for / upgraded later to provide cooling too.

Interestingly, the first major use of UFCH in the UK was to heat public air-raid shelters during WW2 - see https://digital-library.theiet.org/content/journals/10.1049/ji-2.1942.0002 (£)

Posted By: TigoDogI know warm air systems were wide spread in residential buildings in the 70s - but were not popular as I understand it.

It was popular for a decade or so in new-builds in England & Wales, partly because of attractive off-peak electricity tariffs, partly because the alternatives were limited to coal, oil or wood, or town gas in cities. With the 1973 energy crisis the economics looked rather different.

1970s era promo: https://www.youtube.com/watch?v=l9dZQumYqtI

Back on the OP:
An EPC "A" is defined in SAP as an annual energy cost below a certain threshold, works out around £250 for a medium-large house, including heating/water/cooking/lights/etc. The heating part of that will have to be pretty minimal to meet the threshold.

It hardly seems worth spending £10k+ on a heat pump and distribution ducts or ufh. Better just to have a couple of small panel heaters, or heated MHRV?

The alternative would be to spend less on insulation, so consume more heat, but generate the heat cheaper with solar thermal or a heat pump. That would also meet the EPC-"A" cost threshold and deliver the same low operational carbon, but might not comply with building regs insulation levels which were tightened last year, and might not be cheaper overall as the heat pump would need replacing every decade or so.

Posted By: WillInAberdeenAn EPC "A" is defined in SAP as an annual energy cost below a certain threshold, works out around £250 for a medium-large house, including heating/water/cooking/lights/etc. The heating part of that will have to be pretty minimal to meet the threshold.

I don't believe an A is defined so simply, since a common technique for gaming them is to add a load of PV to improve them.

works out around £250 for a medium-large house

The standing charge accounts for about half that! And 1 kWh per day for the other half. What it tells me is that the EPC is a pile of steaming **** and best ignored.

The alternative would be to spend less on insulation, so consume more heat, but generate the heat cheaper with solar thermal or a heat pump.

solar thermal suffers from the same problem as PV - the time of maximum demand is the time of least supply (not coincidentally). So that leaves a heat pump, and even then AIUI we're going to be hard-pressed to generate enough stable electricity, so I continue to believe that minimising energy usage is a laudable social goal.

"Calculating the SAP — or Standard Assessment Procedure — score offers the only government-approved methodology for compliance with Part L of Building Regulations, and for ascertaining the cost of supplying the home with sufficient energy for heating and lighting.

"The score will typically fall between 1-100, and will be calculated based on the construction itself, lighting, heating, and any renewable technologies (such as solar) that will be installed on the property. A score of 100 indicates that the dwelling will have no energy costs, and a score of 100+ means that the property is exporting more energy than it uses."

from https://www.atlanticrenewables.co.uk/news-blog/your-guide-to-meeting-sap-requirements-with-solar.html

"Will I need solar PV panels for the New Part L 2021 SAP?
...
"If you’re looking for a way to pass the SAP calculation with flying colours, then you should consider installing PV panels. PV panels have many benefits that make them an ideal choice for those looking to improve their energy efficiency.

"However, under the new Part L 2021 and SAP 10, PV is now in the new building regulations for the notional assessment. This means that when assessing a dwelling, it will be compared with having solar PV and therefore, if PV is not installed, it will be very difficult to pass the SAP assessment.
...
"Although, this based on using a gas boiler. If you were to install an electric Air Source Heat Pump or Ground Source Heat Pump, then it will be much easier to pass the SAP assessment and there would be no need to install PV! This is due to the high efficiency of the heat pump system."

from https://www.baseenergy.co.uk/knowledge-base/will-i-need-solar-pv-panels-for-the-new-part-l-2021-sap/

Manufacturing anything is damaging for the environment.

And if you believe that UK electricity will be net zero any time in the near future, I've got a brifge you might like to buy. Manufacturing nuclear power stations and solar panels and wind turbines and batteries damages the environment, as does demolishing fossil-fuel power stations. Not to mention costing a lot of money. I'm afraid I don't think the government is competent to deliver it all. So I don't base my planning on assuming it will.

Thanks all for the comments so far - the subscription fee has paid for itself already!

I've created a folder with access to the plans. The proposed site layout shows the orientation: https://drive.google.com/drive/folders/1ThgZxF907N8oUZi3QHArHBuv93cMJbRf?usp=sharing

Posted By: djhI wouldn't try to aim for any particular EPC band. It bears very little relation to the real world

Yes, fair point. This focus comes more from the language we used in our planning application (which took 6 years to gain approval!), and is more of a guide than a requirement. But i take the point that PH standards are a better guide.

Posted By: djhyou'll have trouble meeting PH with the glazing arranged as it is. I can't tell which direction is north.

I think it is unlikely we could achieve PH, there is a neighbouring barn adjacent to ours on the south side, the spots most suitable for glazing are on the north and east faces.

Ducting is possible, I believe, in spite of the timber frame of the main barn. I was imagining something like what Owlman describes, with lower vents for heat/cooling distribution and ceiling vents for return.

Posted By: WillInAberdeenIt hardly seems worth spending £10k+ on a heat pump and distribution ducts or ufh. Better just to have a couple of small panel heaters, or heated MHRV?

An interesting point, I suppose I'm concerned about leaving the building 'under heated' and my dad being cold and grumpy! Would the consultant who provided the U values also instruct how much heating will be required?

Part of the attraction of the HVAC-style systems is that they can provide cool air efficiently too, which may become increasingly important with the way things are going.

Do people have insights on installation costs? I was expecting heat pump + ducting to be significantly cheaper than heat pump + UFH, although no BUS government grant for air-to-air system would counter balance somewhat.

So far I'm reading that either system could work, and it could just be down to costs/personal preference. Are there any particular specialists that members would recommend?

Thanks again all

Posted By: TigoDogDucting is possible, I believe, in spite of the timber frame of the main barn. I was imagining something like what Owlman describes, with lower vents for heat/cooling distribution and ceiling vents for return.

That was why I was keen to discover what size Owlman's ducts actually are.

Posi joists are good, until the pipe is too big!

Would the consultant who provided the U values also instruct how much heating will be required?

Depends entirely on the particular consultant's qualifications etc. You'll need to ask. I would expect the architects to be able to tell you that. But I'd treat any figures with scepticism unless they're produced using PHPP or one of the dynamic models and the user is properly trained.

The drawings don't seem to show a particularly well-insulated building? Also there seem to be multiple SVPs penetrating the thermal envelope; there was a recent thread about SVPs. There are extractor fans; what are the plans for ventilation?

Posted By: djhThe drawings don't seem to show a particularly well-insulated building?

What would be considered well-insulated?

Posted By: djhAlso there seem to be multiple SVPs penetrating the thermal envelope; there was a recent thread about SVPs.

The barn is not on mains sewage, so will have a septic tank.

Posted By: djhThere are extractor fans; what are the plans for ventilation?

I'm keen to use MVHR and was interested how this might work alongside an air-to-air heat pump.

thanks!

Posted By: TigoDogThe barn is not on mains sewage, so will have a septic tank.

We are on a septic tank, That is open vented some are not but best if they are, Our is and an outside loo is as well. All the internal soil pipes have AAV fitted and for extra security all the sink traps also. If you look at this product by McAlpine

https://mcalpineplumbing.com/air-admittance-valves/ventapipe/vp100-ventapipe-100

It allows a large quantity of air in and is approved for use instead of open vented. (That way I was able to avoid unnecessary holes in the roof and unsightly pipes on the house elevations. My BCO was ok with my plan. Coincidentally I have just replaced this valve as the original was sometimes malfunctioning it lasted about 7 years. Taking it off and giving it a shake would fix it for a while.